Using Geoinformatics to Capture Complex Change of a Rock Glacier

Heidelberg research team uses laser scanning and 3D drone data to study an ice-debris mixture in Tyrol

A rock glacier in Tyrol - a downward flowing ice-debris mixture covering more than 40 hectares - is becoming unstable due to rising temperatures and is accelerating towards the valley. A research team from Heidelberg University is involved in the study of the rock glacier "Äußeres Hochebenkar" in the Ötztal Alps of Austria. The geoinformation scientists led by Bernhard Höfle used terrestrial laser scanning and 3D drone data to collect measurements that contribute to decoding the complex dynamics of this permafrost landform. With the aid of newly developed algorithms, the data on the movement and destabilisation can be analysed more precisely.

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Rock glaciers a type of permafrost that can form massive, kilometre-long ice-debris flows. The individual blocks of the downflowing ice-debris mixture can be as large as a small car and can move several tens of metres per year. The movement and changes of the "Äußeres Hochebenkar" rock glacier in Tyrol have been measured and monitored since the 1950s. Using terrestrial laser scanning and 3D drone data, Prof. Höfle and his 3D Geospatial Data Processing (3DGeo) research group at Heidelberg University’s Institute of Geography have been collecting measurement data from the rock glacier front since 2015. The debris-rock surface is scanned centimetre by centimetre and then digitally recorded in 3D. Regular measurements allow detailed changes to be identified and can help to decipher the complex and as yet not fully understood dynamics of this type of permafrost.

To support their investigations, the Heidelberg University geoinformation scientists developed new algorithms that automatically and correctly derive multiple directions of movement and more precise movement rates from the data-rich 3D laser scanning point clouds. This makes it possible for the first time to identify overlapping processes of surface change and to link the changes with potential causes. "For example, we can determine whether material is moving downwards, as in a landslide, or if subsurface ice is being lost at the same time," explains Vivien Zahs, a doctoral candidate and research fellow in the 3DGeo research group.

The three-dimensional change maps compiled by the Heidelberg researchers are a component of an interdisciplinary project. In collaboration with the Austrian Academy of Sciences (ÖAW), the University of Innsbruck (Austria), and the University of Zurich (Switzerland), other observations such as meteorological data were included in the analyses. They are based on a 70-year study of the entire rock glacier. The investigations show that the flow velocity of the "Äußeres Hochebenkar" rock glacier has increased sharply as a result of rising temperatures, states Prof. Höfle. The relatively new and local dataset from his research group provides new insights into the processes that take place at the front of the rock glacier. This knowledge is important, for example, in managing the increasing risks of rock falls on a major access road for Alpine huts further up the valley.

The new algorithms have been integrated into the open-source software "py4dgeo" in collaboration with the Scientific Software Center of Heidelberg University. This tool for analysing geographical changes is openly available to researchers worldwide. The 3D data from the Tyrolean rock glacier are also continuously published as open data. This will allow comparisons of local rock glacier studies and various locations in the Alps.

Research results from the collaboration between the universities in Heidelberg, Innsbruck and Zurich have been published in the journal "Earth Surface Dynamics".

L. Hartl, T. Zieher, M. Bremer, M. Stocker-Waldhuber, V. Zahs, B. Höfle, C. Klug, A. Cicoira: Multi-sensor monitoring and data integration reveal cyclical destabilization of the Äußeres Hochebenkar rock glacier. Earth Surface Dynamics, 11 (1), 117’147 . (28 Feb 2023).